Monitoring the Chemistry Program Change of the Condensate/Feedwater in a Utility Drum Boiler

摘要

For many years, utility chemists removed dissolved oxygen (DO) from feedwater to minimize corrosion. Theory indicated that using an oxygen scavenger/metal passivator would maintain a protective coating of magnetite (Fe3O4) on steel pipe and tube surfaces when a unit was first brought online. Research has shown, however, that this treatment method may lead to several problems. The most notable problem is flow-assisted-corrosion (FAC), in which the reducing environment generated by oxygen scavengers initiates erosion-corrosion at points of flow change. Catastrophic failures in recent years have caused several fatalities. About 30 years ago, European researchers discovered that the controlled addition of small quantities of oxygen to all-ferrous condeiisate/feedwater systems generates a tight oxide film in which the Fe_3O_4 becomes interspersed and overlayed with ferric oxide hydrate (FeOOH). This protective layer is less prone to disruption than Fe3O4, and the oxidizing environment minimizes FAC. Oxygenated treatment (OT) has become popular around the world for once-through boilers, and the technology is finding more applications in drum units.